Versatile habitat conditioning by damselfish cultivating turf algae on giant clams

In this paper, a monitoring and modelling concept for ecological optimized harbour dredging and fine sediment disposal in large rivers is presented. According to the concept, first a preliminary assessment should be performed previous to the dredging and dumping procedure to derive knowledge about the current status in hydrodynamics, morphology and instream habitat quality. During the performance of the maintenance work, a high-resolution monitoring program has to be organized to measure flow velocities, the suspended sediment concentrations and the extent of the occurring plume. These data can then be compared with natural suspended sediment conditions and serve as input data for numerical sediment transport modelling. Furthermore, bathymetric surveys and biotic sampling enable the detection of possible effects of dredging and disposal in the post-dumping stage. Based on sediment transport modelling approaches, short- to mid-term developments of the sediment plume can be predicted with an additional and final habitat evaluation at the end of the project. This concept was applied and optimized during the maintenance work at the case study winter harbour Linz at the Danube River. The findings of the presented study highlight the necessity of integrated monitoring and modelling approaches for harbour dredging especially in large river systems.     

Modelling rainfall and canopy controls on net-precipitation beneath selectively-logged tropical forest

Understanding spatio-temporal patterns in rainfall received beneath tropical forest is required for eco- hydrological modelling of soil-water status, river behaviour, soil erosion, nutrient loss and wet-canopy evaporation. As selective-logging of tropical forest leaves a very complex mosaic of canopy types, it is likely to add to the spatio-temporal complexity of this sub-canopy or net precipitation. As a precursor to addressing this problem, the analysis presented here will examine the two dominant biophysical controls on sub-canopy precipitation. These controls are: (a) the spatial and temporal patterns in above-canopy or gross rainfall, and (b) the rate of wet-canopy evaporation associated with each type of canopy structure created by selective-forestry. For this study, over 400 raingauges were installed within a 10 km² area of lowland dipterocarp forest affected by selective-forestry some 9-years prior to this work. Gauges were located beneath various canopy types and within large openings. The spatial distribution of gross rainfall (monitored within the openings) was modelled using variography, while the effects of different canopy types on sub-canopy preciptation was analysed by comparing 6-month totals. The temporal distribution of gross rainfall over an 11-year record collected at the same site (Danum Valley Field Centre) was modelled with Data-Based-Mechanistic (DBM) approaches. These DBM approaches were also applied to the rainfall time-series of the two adjacent meteorological stations; all three gauges being contained within a 5000 km² region of Eastern Sabah in Malaysian Borneo.Strong diurnal modulation was apparent within gross rainfall for the inland rainforest site, with a distribution consistent with a dominance of local convective rain cells. A similarly strong cycle coincident with the periodicity of the El Niño-Southern Oscillation (ENSO) was present within all of the region's rainfall records, though marked differences in annual and intra-annual seasonality were apparent. The preliminary variogram modelling indicated that a deterministic drift was present within the local-scale gross rainfall data, probably related to local topographic effects. Notwithstanding the need to remove this drift, the work indicated that spatial models of gross rainfall could be identified and used to interpret similar models of net-precipitation. During the ENSO drought-period monitored, the lowland dipterocarp forest allowed 91% of the gross rainfall to reach the ground as throughfall. These rates were, however, reduced to between 80%–86% beneath representative plots of moderately impacted to creeper-covered, highly damaged patches of forest.     

Modelling the effect of forest cover on shallow landslides at the river basin scale

The potential for reducing the occurrence of shallow landslides through targeted reforestation of critical parts of a river basin is explored through mathematical modelling. Through the systematic investigation of land management options, modelling allows the optimum strategies to be selected ahead of any real intervention in the basin. Physically based models, for which the parameters can be evaluated using physical reasoning, offer particular advantages for predicting the effects of possible future changes in land use and climate. Typically a physically based landslide model consists of a coupled hydrological model (for soil moisture) and a geotechnical slope stability model, along with an impact model, such as basin sediment yield. An application of the SHETRAN model to the 65.8-km² Guabalcón basin in central Ecuador demonstrates a technique for identifying the areas of a basin most susceptible to shallow landsliding and for quantifying the effects of different vegetation covers on landslide incidence. Thus, for the modelled scenario, increasing root cohesion from 300 to 1500 Pa causes a two-thirds reduction in the number of landslides. Useful information can be obtained even on the basis of imperfect data availability but model output should be interpreted carefully in the light of parameter uncertainty.     

A review of methods used to measure sediment resuspension

Resuspension of bottom sediments is an important lake-internal process with regard to particle cycling and sedimentation. Current methods to measure sediment resuspension are reviewed, such as optical and acoustical instruments, instantaneous multiple point water samplers, sediment traps, sediment cores and grabs, radiotracers such as Pb²¹⁰, Cs¹³⁷ and Be⁷, mass balance calculations, various modelling approaches, statistical methods (correlation analysis), and laboratory experiments.For the quantification of resuspension, the combined use of sediment traps, sediment cores, near bottom current meters, and turbidity meters to measure suspended and settling particulate matter in the hypolimnion of lakes is recommended; in addition, wind stress, seiches, slumping and sliding, and riverine input may be monitored to elucidate the mechanisms behind the process.     

Multiple indicators of human impacts on the environment in the Pechora Basin,north-eastern European Russia

The Pechora Region (PR) has extensive natural resources supporting forestry, oil and gas industries. The objective of this integrated study was to identify if local and long range pollution and biodiversity impacts were detectable on a regional scale using multi-indicators by selecting paired sites, close to industrial/forestry activities and in ‘reference’ areas (remote from any industrial centers, settlements or commercial activities). Chemistry of lichens, topsoil, lake water and sediments, plus diversity of lichens, birds and aquatic indicators along with landscape analysis were measured at eight sites in the PR to assess local impacts of oil/gas and forestry operations. Furthermore, an analysis of water and sediment chemistry was made at river stations and sites within the Pechora Delta. Local areas around industrial towns of Vorkuta and Usinsk showed increased pollution and decreased biodiversity. Among remote areas, subtle changes in pollution and biodiversity were detected close to oil/gas operations on the Kolva and Ortina Rivers, indicating early signs of environmental impact. Delta analyses showed limited impacts and most other sites remained unmodified reflecting low ecological impacts. Changes in forest landscape structure over large areas were apparently too small to cause significant negative impacts on bird diversity. This was the first attempt showing how multi-indicators can be used over broad spatial scales to assess environmental impacts in the PR.     

Tree-based ensembles unveil the microhabitat suitability for the invasive bleak (Alburnus alburnus L.) and pumpkinseed (Lepomis gibbosus L.): Introducing XGBoost to eco-informatics

Random Forests (RFs) and Gradient Boosting Machines (GBMs) are popular approaches for habitat suitability modelling in environmental flow assessment. However, both present some limitations theoretically solved by alternative tree-based ensemble techniques (e.g. conditional RFs or oblique RFs). Among them, eXtreme Gradient Boosting machines (XGBoost) has proven to be another promising technique that mixes subroutines developed for RFs and GBMs. To inspect the capabilities of these alternative techniques, RFs and GBMs were compared with: conditional RFs, oblique RFs and XGBoost by modelling, at the micro-scale, the habitat suitability for the invasive bleak (Alburnus alburnus L.) and pumpkinseed (Lepomis gibbosus L.). XGBoost outperformed the other approaches, particularly conditional and oblique RFs, although there were no statistical differences with standard RFs and GBMs. The partial dependence plots highlighted the lacustrine origins of pumpkinseed and the preference for lentic habitats of bleak. However, the latter depicted a larger tolerance for rapid microhabitats found in run-type river segments, which is likely to hinder the management of flow regimes to control its invasion. The difference in the computational burden and, especially, the characteristics of datasets on microhabitat use (low data prevalence and high overlapping between categories) led us to conclude that, in the short term, XGBoost is not destined to replace properly optimised RFs and GBMs in the process of habitat suitability modelling at the micro-scale.     

基于SIMWE模型的典型水土保持措施侵蚀阻控路径分析——以通双小流域为例

针对东北黑土区长缓坡地形条件下坡面产汇流集中易加剧土壤侵蚀的问题,本研究基于GIS和SIMWE(SIMulated Water Erosion)模型,引入连通性指数和水深空间分布作为水文连通性与径流路径的衡量指标.通过量化不同典型水土保持措施对土壤入渗速率和地表曼宁糙率的影响,构建梯田数字高程模型(DEM)模拟表征地表...     

Development of a biotic index using stream macroinvertebrates to assess stress from deposited fine sediment

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Retention of suspended sediment and phosphorus on a freshwater delta, South Lake Tahoe, California

The Upper Truckee River and Trout Creek, two major tributaries inflowing to Lake Tahoe, join to form what was historically the largest wetland in the Sierra Nevada mountain range that separates California and Nevada (USA). In the 1950s the delta floodplain of the Upper Truckee River was greatly reduced in area (38%) by urban development and the diversion of the river into a single excavated channel. Conversely, Trout Creek still flows through a wide marsh system with significant overbank flooding before entering Lake Tahoe. This study hypothesized that river channel reaches that are not incised within the delta floodplain retain more sediment and nutrients as a result of greater floodplain connectivity, compared to more incised and excavated reaches. Suspended sediment (SS) and total phosphorus (TP) load data from the delta formed by the Upper Truckee River and Trout Creek were collected using flow stage sensors, turbidometers and depth-integrated samples. During the spring snowmelt flow events monitored in 2003, SS load was reduced by 13–41% for the Upper Truckee River and by 68–90% for Trout Creek. Similar reductions in TP load were observed: 13–32% for the Upper Truckee River and 61–84% for Trout Creek. Monitoring of Trout Creek indicated a reduction in load per unit volume of 20–34% in a moderately incised reach versus a reduction of 51–77% in a non-incised marsh reach containing lagoons, braided channels and backwater areas created by a beaver dam. Smaller particle sizes, <10 μm, were retained in the lower marsh reach with similar efficiencies as larger particle sizes. If retention rates from the Trout Creek portion of the marsh are applied to the Upper Truckee River, sediment loading to Lake Tahoe for 2003 would have been reduced by 917 tons of SS.     

The Influence of Data Resolution on Predicted Distribution and Estimates of Extent of Current Protection of Three ‘Listed’ Deep-Sea Habitats

Modelling approaches have the potential to significantly contribute to the spatial management of the deep-sea ecosystem in a cost effective manner. However, we currently have little understanding of the accuracy of such models, developed using limited data, of varying resolution. The aim of this study was to investigate the performance of predictive models constructed using non-simulated (real world) data of different resolution. Predicted distribution maps for three deep-sea habitats were constructed using MaxEnt modelling methods using high resolution multibeam bathymetric data and associated terrain derived variables as predictors. Model performance was evaluated using repeated 75/25 training/test data partitions using AUC and threshold-dependent assessment methods. The overall extent and distribution of each habitat, and the percentage contained within an existing MPA network were quantified and compared to results from low resolution GEBCO models. Predicted spatial extent for scleractinian coral reef and Syringammina fragilissima aggregations decreased with an increase in model resolution, whereas Pheronema carpenteri total suitable area increased. Distinct differences in predicted habitat distribution were observed for all three habitats. Estimates of habitat extent contained within the MPA network all increased when modelled at fine scale. High resolution models performed better than low resolution models according to threshold-dependent evaluation. We recommend the use of high resolution multibeam bathymetry data over low resolution bathymetry data for use in modelling approaches. We do not recommend the use of predictive models to produce absolute values of habitat extent, but likely areas of suitable habitat. Assessments of MPA network effectiveness based on calculations of percentage area protection (policy driven conservation targets) from low resolution models are likely to be fit for purpose.     

Hydro-sedimentology of the Johnstone River estuary

This paper examines the physical consequences of increased catchment sediment yields on the sediment budget and the hydrodynamic setting of the South Johnstone River estuary in North Queensland. A combined study involving hydrological monitoring, assessment of sediment sources, estimation of riverine sediment budget and hydro-sedimentological numerical modelling for estuarine sediment transport is currently underway. Initial field and laboratory observations indicate that the sediment delivery from highly erosion-prone sugar cane cultivations in the tropical catchment has increased dramatically during the last 10 years. This has subsequently given rise to elevated flood levels in both the lower and upper catchment areas, as well as significant modifications to the river bed morphology.     

Environmetric time-series analysis: modelling natural systems from experimental time-series data

Using the modelling of solute transport in flowing media as an example, this paper outlines the main aspects of a systematic approach to the modelling of natural systems from experimental time-series data. The objective of the approach, which exploits sophisticated methods of recursive parameter estimation, is to produce a parametrically efficient, data-based model which is both physically meaningful and statistically well defined. Although the proposed methodology has its origins in systems and control theory and may be unfamiliar to some natural scientists, it has been developed and refined for use with natural environmental systems over the past 20 years, and has wide application potential in areas such as biology and ecology. In this sense, the paper is intended to introduce the more general reader to the topic, in the hope that the tutorial review and practical examples will stimulate interest and encourage reference to the many publications cited in the paper. The practical examples are concerned with the modelling of pollutant dispersion in stream channels: phloem translocation and carbon partitioning in plants: and rainfall-streamflow modelling in a river catchment.     

Abiotic influences on dissolved oxygen in a riverine environment

Dissolved oxygen (DO) is an important parameter in riverine health. Periphyton and/or macrophytes are frequently the drivers behind the fluctuation of DO levels in aquatic environments; however, the effects of abiotic and biotic factors on biomass and in turn on DO may be variable from river to river. The objective of this paper is to understand which factors govern DO levels in terms of daily minimum DO (DO_min) and daily DO variation (ΔDO) in a major wastewater-impacted river using statistical data analysis and modeling. Both climatic conditions (reflected in water temperature) and hydrometric conditions (flow) were major factors influencing DO_min and ΔDO. The effect of flow on DO_min and ΔDO was discontinuous, depending on the flow magnitude. Nutrient loading from wastewater effluent was not identified to have a significant impact on a daily basis; however, their role over large time scales is unclear. In the data-driven modeling approaches, the non-linear approach using multiple-layer perceptron neural network, which has very flexible architecture, was superior to the linear approach used (multiple linear regression). Although nutrients are likely related to the DO_min and ΔDO, flow and temperature were sufficient to obtain robust prediction in the data-driven modeling. This approach is useful to model and understand complicated processes when their governing mechanisms are not well presented in conceptual- or physically based models.     

Efficiency and uncertainties in micro- and mesoscale habitat modelling in large rivers

Habitat modelling has become an increasingly important tool in river sciences to evaluate impacts on running waters and to predict the effects of river restoration in the context of the European Water Framework Directive which aims to reach a good ecological status by 2015. In a scaling framework like the River Scaling Concept, micro- and mesoscale habitat modelling hierarchically integrate point-/local-scale abiotic processes like grain sorting, initiation of sediment transport, bedform development and braiding with biological processes like spawning, daily and seasonal movements, feeding and shifting to refuge habitats. The paper, along with application results, shows that micro- and mesoscale habitat models are complementary especially for large river systems. Overall possibilities, restrictions and future development are discussed. Both rely on dynamic abiotic modelling as a basis as well as on biological data. In future, especially for large rivers, habitat modelling should be addressed on both scales (micro-/meso-) with the main focus on site-specific efficiencies (e.g. minimum efforts) and uncertainties (e.g. transferring suitability indices).     

Distributional modelling and parsimony analysis of endemicity of Senecio in the Mediterranean-type climate area of Central Chile

Aim Floristic blocks and areas of endemism resulting from a parsimony analysis of endemicity (PAE) using raw floristic data versus data generated from distributional modelling for 130 species in the genus Senecio Tourn. ex L. distributed in the Mediterranean‐type climate area of Central Chile were compared, and the results were used to identify conservation priorities for the flora of the region. Location Central Chile, between 30° and 38° S. Methods Using herbarium records, a species × area matrix consisting of presence/absence data was constructed from a 0.5° × 0.5° grid. Distributional modelling techniques incorporating vegetation formations, elevation and the contagion index were used to interpolate floristic composition of poorly known areas. Parsimony analysis of endemicity was used to identify floristic blocks and areas of endemism. Results Using the number of most parsimonious trees as an index, distributional modelling greatly optimized the results of the PAE analysis. Three floristic blocks and four areas of endemism were suggested based on the PAE results using potential distribution data not incorporating the contagion index, while four blocks and two areas of endemism were suggested from the PAE results using potential distribution data incorporating the contagion index. Floristic blocks for the northern coast, southern Andes, and northern/central Andes were found, with some blocks showing divisions within them representing distinct geographic subunits. Major breaks between and within floristic blocks were identified at 32.5°–33° S and 34.5°–35° S. Main conclusions The floristic blocks identified with the distributional modelling and PAE correspond well to results from some previous studies and support hypothesized biogeographic divisions within Central Chile. The results were similar to those obtained from parallel analysis of the entire tree flora of Central Chile. The vegetative formation‐based distributional modelling produced robust and reproducible results when used along with PAE, especially when the contagion index was incorporated, and is a useful technique for area classification. The results demonstrate the utility of Senecio as an indicator genus for biogeography and conservation in southern South America.     

Accounting for uncertainty in marine reserve design

Ecosystems and the species and communities within them are highly complex systems that defy predictions with any degree of certainty. Managing and conserving these systems in the face of uncertainty remains a daunting challenge, particularly with respect to developing networks of marine reserves. Here we review several modelling frameworks that explicitly acknowledge and incorporate uncertainty, and then use these methods to evaluate reserve spacing rules given increasing levels of uncertainty about larval dispersal distances. Our approach finds similar spacing rules as have been proposed elsewhere – roughly 20–200 km – but highlights several advantages provided by uncertainty modelling over more traditional approaches to developing these estimates. In particular, we argue that uncertainty modelling can allow for (1) an evaluation of the risk associated with any decision based on the assumed uncertainty; (2) a method for quantifying the costs and benefits of reducing uncertainty; and (3) a useful tool for communicating to stakeholders the challenges in managing highly uncertain systems. We also argue that incorporating rather than avoiding uncertainty will increase the chances of successfully achieving conservation and management goals.     

Landscape scenario modelling of vegetation condition

Summary   Landscape scenario modelling is a useful aid to planning for biodiversity conservation. Vegetation condition modelling is increasingly being integrated into such analysis. Model complexity and model uncertainty are critical factors that must be addressed when tailoring vegetation condition modelling to individual applications. We describe three approaches that we have used to compare the effects of different landscape scenarios on vegetation condition. The first is a simple land-use–condition approach where vegetation condition is determined solely by land use. The second is a land-use–regeneration approach that introduces transition functions to model vegetation condition dynamics associated with land use change. The third is a threat–regeneration approach, which models vegetation condition dynamics based on the interaction between regeneration and a range of mapped threats. The three approaches represent a progression towards increased refinement and realism, but also increased complexity and data requirements. We examine the relative usefulness of the three approaches and conclude that there is no single 'silver bullet' solution but recommend judicious matching of approaches to applications within a collaborative and adaptive setting.     

Identifying Pathways for Improving Household Food Self-Sufficiency Outcomes in the Hills of Nepal

Maintaining and improving household food self-sufficiency (FSS) in mountain regions is an ongoing challenge. There are many facets to the issue, including comparatively high levels of land fragmentation, challenging terrain and transportation bottlenecks, declining labor availability due to out-migration, and low technical knowledge, among others. Using a nonparametric multivariate approach, we quantified primary associations underlying current levels of FSS in the mid-hills of Nepal. A needs assessment survey was administered to 77 households in Lungaun (Baglung District), Pang (Parbat District), and Pathlekhet (Myagdi District), with a total of 80 variables covering five performance areas; resulting data were analyzed using Classification and Regression Trees. The most parsimonious statistical model for household FSS highlighted associations with agronomic management, including yields of maize and fingermillet within a relay cropping system and adoption of improved crop cultivars. Secondary analyses of the variables retained in the first model again focused primarily on crop and livestock management. It thus appears that continued emphasis on technical agricultural improvements is warranted, independent of factors such as land holding size that, in any case, are very difficult to change through development interventions. Initiatives to increase household FSS in the mid-hills of Nepal will benefit from placing a primary focus on methods of agricultural intensification to improve crop yields and effective technology transfer to increase adoption of these methods.     

Geochemical and physical characteristics of river and lake [2pt] sediments at Naivasha,Kenya

Prior studies on Lake Naivasha relevant to understanding sediment dynamics include a bathymetric map, a paleolimnological study of fossil invertebrate assemblages in lake sediment, an overview of lake level fluctuations throughout the 20th century, and identification of a dynamic assemblage of macrophyte zones that has responded both to these changes in lake level and to more recent, alien species. Sediment samples collected from the rivers systems and the lake were examined physically and chemically. River sediment characteristics reflect geology and geomorphological processes in the catchment, whereas lake sediment stratigraphy has responded to past lake level changes. Such changes have caused significant changes in aquatic vegetation assemblages. Present day sediment dynamics in the lake are governed by the presence of river point sources in the north and wave-induced re-suspension, such that sediments introduced by rivers are transported in easterly and southerly directions, and are eventually deposited in the eastern, central and southern parts of the lake. Sedimentary deposition is also occurring in northern areas that once were protected by papyrus swamp vegetation but now only have a narrow fringe, highlighting the important role of swamp vegetation in filtering out suspended particulates and thereby controlling water quality in the lake. Geochemical analyses of river and lake sediments indicate that they represent fairly undisturbed background conditions. Higher-than-expected concentrations of cadmium, iron, nickel and zinc found in both river and lake sediment are likely to derive from volcanic rocks and/or lateritic soils found in the lake catchment.